Connector does not work when using AoG conversations.

Hi, Im using AoG to store conversations in my fulfillment

https://github.com/dialogflow/dialogflow-fulfillment-nodejs/tree/master/samples/actions-on-google

Some of the sample code here for example - the current implementation of the dialogflow connector does not support the conv() object which is key to all AoG requests - This is used for suggestion chips/displaying carousels/user storage in our fulfillment code.

A call from Botium however does not have this object and breaks our fufillment code with the below error:

`TypeError: Cannot read property 'user' of null
at exports.dialogflowFirebaseFulfillment.functions.https.onRequest`

And i receive the following error from Dialogflow

` webhookStatus:
botium-connector-dialogflow { details: [],
botium-connector-dialogflow code: 13,
botium-connector-dialogflow message: 'Webhook call failed. Error: 500 Internal Server Error' } } +658ms`

Is this going to be supported any time soon?

Start by reproducing the failure with the Actions on Google samples linked in the issue and a Botium Dialogflow call. Compare the connector's request handling with the sample fulfillment expectations around the conv() object and user data. Done means AoG fulfillment code using conv() no longer fails and the webhook request succeeds.

Written by the indexing model from the issue text.